1. Field of the Invention
The present invention relates to a lead oxide based piezoelectric ceramic composition, for example to a piezoelectric ceramic composition to be used as a piezoelectric member in piezoelectric resonators, piezoelectric filters, piezoelectric transformers or piezoelectric actuators. The present invention also relates to a piezoelectric resonator, a piezoelectric transformer and a piezoelectric actuator using the piezoelectric ceramic composition.
2. Description of the Related Art
Pb(Ti, Zr)03 based piezoelectric ceramics have been used for communication system filters, CPU clocks, actuators or sensors taking advantage of piezoelectric effects. Piezoelectric ceramics based on plural components such as Pb(Ti, Zr)O3xe2x80x94PB(Mn1/3Sb2/3)O3 have been also used for improving electrical characteristics.
However, Pb has been apt to be evaporated as PbO by firing in the conventional Pb(Ti, Zr)O3 based piezoelectric ceramics since they should be fired at a high temperature. Consequently, the electrical characteristics have been often deteriorated, or the electrical characteristics among the piezoelectric ceramics obtained showed a large distribution. In other words, a piezoelectric ceramic that can exhibit desired electric characteristics could not be securely manufactured, making it difficult to design various devices using the piezoelectric ceramics.
Accordingly, it is an object of the present invention to provide a piezoelectric ceramic composition for making it possible to obtain a piezoelectric member having small variation of electrical characteristics by suppressing evaporation of Pb by firing.
An another object of the present invention is to provide a piezoelectric resonator, piezoelectric transformed and piezoelectric actuator using the piezoelectric ceramic composition as hitherto described.
The present invention for solving the foregoing problems provides a piezoelectric ceramic composition with a perovskite structure of an oxide containing Pb, Ti, Zr, Ma (Ma denotes at least one of Cr, Mn, Fe and Co) and Md (Md denotes at least one of Nb, Sb, Ta and W), wherein z is within a range of 0.50 less than z less than 1.00 with the proviso that the total content of Ma is a, and the contents of Sb, Nb, Ta and W of the elements Md are b, c, d and e, respectively, satisfying the relation of a/(b+c+d+2e)=z.
A part of Pb may be replaced by Ba, Ca, Sr, La, Nd and Ce within a range not to compromise the objects of the present invention. The elements of Ma and Md may be mingled with lead titanate zirconate to form a solid solution of a composite oxide, or they may be used as pure oxides.
Preferably, u in the perovskite structure represented by AuBO3 falls within a range of 0.98xe2x89xa6uxe2x89xa61.02 (wherein A is composed of a total of Pb and substituted elements when Pb or a part of Pb is replaced by Ba and the like, and B is composed of Ti, Zr, Ma and Md) in order to obtain better piezoelectric characteristics.
Preferably, x is within a range of 0.45xe2x89xa6xxe2x89xa60.65 with the proviso that the ratio of Ti and Zr is x:(1xe2x88x92x) in order to obtain better piezoelectric characteristics.
It is also preferable that Si is added in a proportion of about 0.005 to 0.1% by weight when converted into SiO2 relative to a combined proportion of 100% by weight of Pb, Ti, Zr, Ma and Md.
A piezoelectric member comprising the piezoelectric ceramic composition according to the present invention may be used for the piezoelectric resonator according to the present invention.
Also, a piezoelectric member comprising the piezoelectric ceramic composition according to the present invention may be used for the piezoelectric transformer according to the present invention.
Also, a piezoelectric member comprising the piezoelectric ceramic composition according to the present invention may be used for the piezoelectric actuator according to the present invention.